转载:http://blog.sina.com.cn/s/blog_629e606f01014d4b.html
ComboBox最经常使用的事件就是SelectedIndexChanged。但在将ComboBox绑定到某个数据源的过程中,会触发SelectedIndexChanged
事件,而这个时候用户并没有选择内容,其SelectedValue也不是对应字段的值。那么时写在SelectedIndexChanged中的处理代码就会因为SelectedValue的内容不正确引发异常。
一般网上找到的方法是添加一个标记位,在绑定前设置为false,绑定完成后设置回true。
void BindComboBox()
{
flag=false;
ComboxBox1.ValueMember="ValueColumn";
ComboxBox1.DisplayMember="DisplayColumn";
ComboxBox1.DataSource=DataTable1;
flag=true;
}
{
flag=false;
ComboxBox1.ValueMember="ValueColumn";
ComboxBox1.DisplayMember="DisplayColumn";
ComboxBox1.DataSource=DataTable1;
flag=true;
}
private void ComboxBox1_SelectedIndexChanged(object sender, EventArgs e)
{
if(flag)
{
//Do something
}
}
另外还有一种办法,就是在绑定前,将SelectedIndexChanged的委托去掉,等绑定完成后,再添加事件委托。{
if(flag)
{
//Do something
}
}
void BindComboBox()
{ //去除委托
ComboBox1.SelectedIndexChanged -= new EventHandler(ComboBox1_SelectedIndexChanged);
ComboBox1.DataSource = null;
ComboBox1.ValueMember = "ValueColumn";
ComboBox1.DataSource = DataTable1;
//添加委托
ComboBox1.SelectedIndexChanged += new EventHandler(ComboBox1_SelectedIndexChanged);
ComboBox1.DisplayMember = "DisplayColumn";
}
两种方法都可以,但是之间的优劣暂时没去比较。感觉好像处理一下委托会好点。因为这种办法真的减少了事件的激发次数。{ //去除委托
ComboBox1.SelectedIndexChanged -= new EventHandler(ComboBox1_SelectedIndexChanged);
ComboBox1.DataSource = null;
ComboBox1.ValueMember = "ValueColumn";
ComboBox1.DataSource = DataTable1;
//添加委托
ComboBox1.SelectedIndexChanged += new EventHandler(ComboBox1_SelectedIndexChanged);
ComboBox1.DisplayMember = "DisplayColumn";
}
不知道还有没有其他解决方案呢?
另,贴上一段完整的代码例子。这个例子是访问SqlServer数据库的AdventureWorks,通过ProductCategory和ProductSubCategory两级目录分类去查看Product表的内容。分别使用两个ComboBox和DataGridView完成数据绑定。效果就是选择之后会联动改变相关内容。
public partial class frmProduct : Form
{
DataSet DS = new DataSet();
String ConnectionString = "integrated security=true; database=AdventureWorks; server=localhost; ";
public frmProduct()
{
InitializeComponent();
}
private void frmProduct_Load(object sender, EventArgs e)
{
SqlDataAdapter da = new SqlDataAdapter("select ProductCategoryID,[Name] from Production.ProductCategory", ConnectionString)
;
cbbCategories.SelectedIndexChanged -= newEventHandler(cbbCategories_SelectedIndexChanged);
da.Fill(DS, "ProductCategory");
cbbCategories.DataSource = null;
cbbCategories.ValueMember = "ProductCategoryID";
cbbCategories.DataSource = DS.Tables["ProductCategory"];
cbbCategories.SelectedIndexChanged += newEventHandler(cbbCategories_SelectedIndexChanged);
cbbCategories.DisplayMember = "Name";//这句放在事件委托之后才会有联动效果,下同
}
private void cbbCategories_SelectedIndexChanged(object sender, EventArgs e)
{
SqlDataAdapter da = new SqlDataAdapter("select ProductSubCategoryID,[Name] from Production.ProductSubCategory where ProductCategoryID=" + cbbCategories.SelectedValue.ToString(), ConnectionString)
;
if (DS.Tables["ProductSubCategory"] != null)
{
DS.Tables["ProductSubCategory"].Clear();
}
da.Fill(DS, "ProductSubCategory");
cbbSubCategories.SelectedIndexChanged -= newEventHandler(cbbSubCategories_SelectedIndexChanged);
cbbSubCategories.DataSource = null;
cbbSubCategories.ValueMember = "ProductSubCategoryID";
cbbSubCategories.DataSource = DS.Tables["ProductSubCategory"];
cbbSubCategories.SelectedIndexChanged += newEventHandler(cbbSubCategories_SelectedIndexChanged);
cbbSubCategories.DisplayMember = "Name";
}
private void cbbSubCategories_SelectedIndexChanged(object sender, EventArgs e)
{
if (cbbSubCategories.SelectedIndex == -1)
return;
SqlDataAdapter da=new SqlDataAdapter("select * from Production.Product where ProductSubCategoryID=" + cbbSubCategories.SelectedValue.ToString(), ConnectionString);
dgvProduct.DataSource = null;
if (DS.Tables["Product"] != null)
DS.Tables["Product"].Clear();
da.Fill(DS, "Product");
dgvProduct.DataSource = DS.Tables["Product"];
}
}
{
DataSet DS = new DataSet();
String ConnectionString = "integrated security=true; database=AdventureWorks; server=localhost; ";
public frmProduct()
{
InitializeComponent();
}
private void frmProduct_Load(object sender, EventArgs e)
{
SqlDataAdapter da = new SqlDataAdapter("select ProductCategoryID,[Name] from Production.ProductCategory", ConnectionString)
;
cbbCategories.SelectedIndexChanged -= newEventHandler(cbbCategories_SelectedIndexChanged);
da.Fill(DS, "ProductCategory");
cbbCategories.DataSource = null;
cbbCategories.ValueMember = "ProductCategoryID";
cbbCategories.DataSource = DS.Tables["ProductCategory"];
cbbCategories.SelectedIndexChanged += newEventHandler(cbbCategories_SelectedIndexChanged);
cbbCategories.DisplayMember = "Name";//这句放在事件委托之后才会有联动效果,下同
}
private void cbbCategories_SelectedIndexChanged(object sender, EventArgs e)
{
SqlDataAdapter da = new SqlDataAdapter("select ProductSubCategoryID,[Name] from Production.ProductSubCategory where ProductCategoryID=" + cbbCategories.SelectedValue.ToString(), ConnectionString)
;
if (DS.Tables["ProductSubCategory"] != null)
{
DS.Tables["ProductSubCategory"].Clear();
}
da.Fill(DS, "ProductSubCategory");
cbbSubCategories.SelectedIndexChanged -= newEventHandler(cbbSubCategories_SelectedIndexChanged);
cbbSubCategories.DataSource = null;
cbbSubCategories.ValueMember = "ProductSubCategoryID";
cbbSubCategories.DataSource = DS.Tables["ProductSubCategory"];
cbbSubCategories.SelectedIndexChanged += newEventHandler(cbbSubCategories_SelectedIndexChanged);
cbbSubCategories.DisplayMember = "Name";
}
private void cbbSubCategories_SelectedIndexChanged(object sender, EventArgs e)
{
if (cbbSubCategories.SelectedIndex == -1)
return;
SqlDataAdapter da=new SqlDataAdapter("select * from Production.Product where ProductSubCategoryID=" + cbbSubCategories.SelectedValue.ToString(), ConnectionString);
dgvProduct.DataSource = null;
if (DS.Tables["Product"] != null)
DS.Tables["Product"].Clear();
da.Fill(DS, "Product");
dgvProduct.DataSource = DS.Tables["Product"];
}
}